HELP!!!1965 Merc 500 no reverse

[Skinless76]

This is my first post to iboats and have accumulated a wealth of knowledge about boats and boating from just reading the posts located here. I am posting because I can not get my 1965 merc 500 to go into reverse. Let me explain a little more. It does go into forward gear and neutral. The lever does cause the engine to rev up in reverse but the prop does not spin and there is no sound of the motor even attempting to go into gear. It has not had any type of lower unit work done on it as well. Any help would be greatly appreciated. I am new to boating and this is my first boat and motor. Thanks for any help that can be offered.